Measles remains a major worldwide health problem. The primary complications associated with this infection are pneumonia, diarrhea, and postinfectious encephalomyelitis. Previous studies have shown that skin test responses and mitogen-induced lymphoproliferative responses are suppressed for approximately 4 weeks after the onset of the rash. The effect of this virus infection on the immune system of the infected individual may play a prominent role in the development of these complications. The objective of this proposal is to further define the relationship between measles virus infection and functional alterations in the immune system and the following specific aims are proposed: (1) To determine whether peripheral blood mononuclear cells are infected with measles virus in vivo using fractionated cells and dot blot hybridization. (2) To further define monocyte abnormalities in natural and in vitro-induced measles virus infections using in vitro stimulation of peripheral blood mononuclear cells. Production of IL-1, PGE2, and other suppressive factors will be measured. (3) To determine the response of lymphocytes from patients with measles and in vitro measles virus-infected lymphocyte cultures to mitogen stimulation. The production of IL-2, soluble IL-2 receptor, - interferon and the expression of surface activation markers (Tac, T10, T9 and HLA-DR) in the presence and absence of indomethacin and supplemental IL-1 will be measured. (4) To identify the inflammatory cells present and the expression of activation markers at sites of infection by immunocytochemical staining of autopsy tissue from patients with acute fatal measles. (5) To identify the proliferating cells in the peripheral blood of measles patients by combined autoradiography and immuncytochemical staining. (6) To characterize the cytotoxic cells during acute measles by assaying for natural killer cell activity and cytotoxic T cell activity and generating functional clones of T lymphocytes.